Nonwoven filtration media for the removal of solid particulate matter from gases have been proposed in the past and are commercially available. The most common nonwoven filtration medium produced in the past has been of the surface type wherein the ingress of deleterious solid particles suspended in the gas undergoing treatment is precluded and such unwanted contamination is deposited at the surface of the filtration medium. Such a surface filtration medium has had the disadvantage of a limited life that often has necessitated replacement at somewhat frequent intervals particularly if a large concentration of solid particulate matter is encountered. Under such circumstances as solid particulate matter builds up exclusively at the surface of the filtration media, it eventually precludes the further passage of any substantial quantity of the gas that is being subjected to filtration.
In recent years the use of fuel-injection systems having close tolerances in conjunction with internal combustion engines has created additional demands for a relatively inexpensive disposable filtration medium that will perform well over a variety of environments to accomplish the substantial removal of solid particles of a wide range of sizes that are suspended in the air stream that is directed to the engine. Such severe filtration demands must also be balanced with a desire to extend the period of time between routine maintenance procedures and filter replacement. Accordingly, it has been proposed in the past to substitute in some instances the use of depth filtration media instead of surface filtration media. Such depth filtration media exhibit a more open three-dimensional internal structure to effectively trap the solid particles throughout the cross-section of the filtration medium rather than exclusively at the surface of the filtration medium.
The pleating of filtration media is recognized to increase the surface area within a given three-dimensional area and to thereby increase the useful life of the media. It further is recognized that resin impregnated paper filters when situated adjacent fuel-injected engines which operate at higher temperatures may become embrittled during usage in such environment.
In the past a multi-layered nonwoven pleated depth filtration medium for automotive applications having a thickness of approximately 106 mils has been available from Toyobo Co., Ltd. of Oska, Japan and Purodenso of Jackson, Tenn. Such filtration medium is believed to consist of a top layer of approximately 0.9 oz./yd..sup.2 polyvinyl alcohol staple fiber web, an intermediate layer of approximately 3 oz./yd..sup.2 polyethylene terephthalate staple fiber web, and a backside of approximately 2 oz./yd..sup.2 of a discontinuous cellulosic fiber paper or web. The three layers described above are needle-punched and the backside is coated with approximately 30 percent by weight based on the total weight of the filtration medium of an acrylate polymer. The pleatability of such filtration medium is understood to be influenced by variations in its moisture content. For instance, both the polyvinyl alcohol staple fibers and cellulosic fibers present therein have a tendency to retain a substantial quantity of water from the ambient atmosphere.
It is an object of the present invention to provide a nonwoven multi-layered composite article of the indicated structure that has been found to be well suited for service as a depth gaseous filtration medium.
It is an object of the present invention to provide a nonwoven multi-layered composite article of the indicated structure that is capable of readily undergoing pleating on a stable basis to form a pleated depth gaseous filtration medium while retaining permeability for gaseous filtration.
It is an object of the present invention to provide an improved nonwoven multi-layered composite article of the indicated structure that is stable in nature and is capable of efficient service for an extended period of time as a depth gaseous filtration medium.
It is an object of the present invention to provide a nonwoven multi-layered composite filtration medium that can exhibit an equivalent or superior dust holding capacity when compared to that being marketed by Toyobo Co., Ltd. and Purodenso while being of a lesser thickness thereby making possible or more efficient filtration medium per unit of cross-sectional area.
It is an object of the present invention to provide a non-woven multi-layered composite filtration medium that does not require the relatively high level resin coating employed in the product marketed by Toyobo Co., Ltd. and Purodenso.
It is another object of the present invention to provide an improved nonwoven multi-layered composite article of the indicated structure which is capable of no substantial moisture retention and is not influenced by changes in the relative humidity of the gas that passes therethrough.
It is a further object of the present invention to provide an automotive air filter that incorporates the pleated nonwoven composite article of the present invention therein.
These and other objects, as well as the scope, nature and utilization of the invention will be apparent to those skilled in the art from the following description and appended claims.